Page 88 - University of Pretoria Research Review 2017

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Modelling wood formation and its evolution
Biopolymers produced in the wood of trees (e.g. cellulose, hemicelluloses and lignin) serve as raw material for many commercial high-end value derivatives.
Fast-growing tree species such as Eucalyptus are important sources of biomass for these polymers worldwide, and South Africa is a major player in this context. The forestry industry is also gaining relevance in the emerging global bio-based/green economy,
due to the immense contribution it can make towards renewable bioenergy and biomaterials such as biodegradable polymers, surfactants, bio-bitumen
or cross-laminated timber for sustainable building materials.
The research group of Dr Eshchar Mizrachi focuses on reverse engineering of wood formation as a system,
to understand how it works and which key points are available for rational intervention and improvement through biotechnology. Mizrachi’s specific interest
has been in constructing a model of the regulatory network (genes, proteins and pathways) that plays a role in influencing wood development, and identifying candidate genes and pathways for biotechnological improvement of trees (e.g. applied via breeding using molecular selection tools, or genetic modification).
The main technology applied in their research is second- generation transcriptome sequencing technology, which has allowed unprecedented insight into the dynamics
of expressed genes. Other ‘omics techniques are also used to complement the transcriptomic research. Applying these technologies at a population level is filling in the gap between genetic variation and complex wood properties. By integrating various layers of biology, the research group published a study in 2017 that uses a novel methodology to link the variation of genes and entire pathways to industrially relevant tree growth, wood formation and wood processing traits. The publication was a collaboration between Mizrachi and Professor Zander Myburg, who established the Forest Molecular Genetics programme at UP, and Professors Kathleen Marchal and Yves van de Peer, both Extraordinary Professors at UP*.
Plastids (specialised ‘metabolic factory’ compartments within each plant cell) are the reason almost all plants are green and can produce sugars using light, water and CO2, but they are also responsible for the starch
in potatoes and many of the vitamins in fruit and vegetables. Mizrachi and colleagues, especially the work of PhD student, Desre Pinard, also study a hitherto largely ignored element of wood biology – the role of plastids in wood development. Plastids are a key carbon partitioning point between polysaccharide and phenolic biopolymers, and greater understanding of how carbon metabolic flux is regulated in these compartments is key to developing advanced biotechnology solutions to biomass-related crops.
As a developmental system, xylogenesis (wood formation) offers an attractive model for understanding complex systems and their response to perturbations. Mizrachi and his group (especially Danielle Roodt, a PhD student) are studying the evolution of this system by comparing dozens of plant genomes, as well as generating new genomic resources for and analysing under-studied ‘missing link’ plants, such as Ginkgo, cycads and the herb Ephedra.
* Mizrachi E et al., (2017). Network-based integration of systems genetics data reveals pathways associated with lignocellulosic biomass accumulation and processing. PNAS 114(5):1195-1200.10.1073/pnas.1620119114